\begin{abstract}

%When cloud user's application run in the virtual network, network problems may happen from various hierarchies. However, cloud platforms provide little support for the tenant to diagnose the network problems. Network virtualization hides the infrastructure to the tenant as well as prevent deploying most of the network diagnostic tools. We propose a Virtual Network Diagnosis 
%(VND) framework which provide virtual network diagnosis service to the tenant. The tenant can collect, parse and analyze their network traffic through an abstract interface to diagnose their virtual networks, and the cloud administrator can control access without exposing infrastructure and other tenants' information unnecessarily. We address the design challenges and solutions like abstractions, overhead, scalability and flow disambiguating. Our preliminary evaluation shows that VND data collection does not impact the existing network application traffic and the diagnostic tasks can be executed quickly.

  Today's cloud network platforms allow tenants to construct
  sophisticated virtual network topologies among their VMs on a shared
  physical network infrastructure. However, these platforms provide
  little support for tenants to diagnose problems in their virtual
  networks.  Network virtualization hides the underlying
  infrastructure from tenants as well as prevents deploying existing
  network diagnosis tools. This paper makes a case for providing
  virtual network diagnosis as a service in the cloud. We identify a
  set of technical challenges in providing such a service and propose
  a Virtual Network Diagnosis (VND) framework.  VND exposes abstract
  configuration and query interfaces for cloud tenants to troubleshoot
  their virtual networks. It controls software switches to collect
  flow traces, distributes traces storage, and executes distributed
  queries for different tenants for network diagnosis. It reduces the
  data collection and processing overhead by performing local flow
  capture and on-demand query execution. 
  %Our evaluation shows the feasibility of providing a virtual network diagnosis service in the cloud. VND is prompt to respond tenant's diagnosis request and introduces acceptable overhead.
  Our experiments validate VND's functionality and shows its feasibility 
  in terms of quick service response and acceptable overhead; our simulation
  proves the VND architecture scales to the size of a real data center network.
  %\aditya{rephrase las sentence with actual results}
  



\end{abstract}
